Apparatus for and method of generating and superheating steam



1961 J. R. MURRAY ETAL 3,007,456

APPARATUS FOR AND METHOD OF GENERATING AND SUPERHEATING STEAM Filed July13, 1956 LOW PRESS. STM.SOURCE INVENTORS Jullan R. Murray 42 BY JacksonE. O'Connell ATTORNEY 3,007,456 APPARATUS FOR AND METHOD OF GENER- ATINGAND SUPERHEATING STEAM Julian R. Murray, Skokie, and Jackson E.OConnell, Elmhurst, 11]., assignors to The Babcock & Wilcox Company, NewYork, N.Y., a corporation of New Jersey Filed July 13, 1956, Ser. No.597,655 8 Claims. (Cl. 12233) This invention relates to the art of steamgeneration and steam superheating. More particularly, the inventionrelates to the generation of high pressure (i.e. 2400 psi) steam in afuel fired unit including *a gas heated steam superheater, the initialsuperheating of relatively low pressure steam (350 psi.) by indirectheat transfer involving the condensing 'of all of the high pressuresteam, the return of the condensate to the high pressure steamgeneration, the subsequent superheating of the low pressure steam in aplurality of stages in the gas heated superheater of the unit, andprovisions whereby the gas heated superheater of the unit may,alternatively, superheat the high pressure steam when low pressure steamis not available, the latter provisions functionally eliminating theinitial superheating by indirect heat exchange and effecting steam flowdirectly from the zone of generation of high pressure steam to the gasheated superheater of the unit.

The steam generating and steam superheating unit of the invention isparticularly applicable to a power plant having a plural pressure stagesteam turbine means with a lower pressure stage of the turbine meansreceiving 1100 F. steam at a relatively low pressure (i.e. 350 p.s.i.aor 600 p.s.i.a.) and generated by a nuclear reactor, and with the highpressure stage of the turbine receiving relatively higher pressuresteam.

The invention is exemplified in a steam generating and superheating unitin which relatively low pressure steam derived from a source independentof the unit is superheated in a plurality of stages in a separatelyfired superheater. The latter preferably includes a high pressure steamgenerating section in which the steam is generated predominantly in thewall tubes of a fuel fired furnace, Saturated steam from this highpressure source is adapted to transmit heat by indirect heat exchange tothe low pressure steam to superheat the latter in a first stage ofsuperheating, with high pressure steam being condensed in thissuperheating stage. The low pressure steam heated in this initialsuperheating stage then passes through successive other superheatingstages formed by the gas heated superheating means of theseparately'fired superheater, or high pressure steam unit. v

The invention may be regarded as including a separately firedsuperheater burning a fossil fuel or a slag forming fuel at combustiontemperatures in excess of 2200 F. and having a high capacity forsuperheating relatively low pressure steam. The separately firedsuperheater of the invention is characterized by high availability andlow furnace chamber wall maintenance by its inclusion in the furnacechamber walls adjacent the active combustion zone of steam generatingtubes operating at the saturation temperature of the high pressuresteam, while the wall portions of the fumaoe chamber beyond the activecombustion zone in a gas flow sense contain radiant superheater walltubes forming one stage or part of the superheating means and normallyreceiving the low pressure steam from the independent steam generatingsource.

The invention particularly involves means whereby the power plant may beoperated solely by steam generated in the unit when the nuclear reactoror other independent source of relatively low pressure steam is shutdown.

Under these circumstances, the steam generated in the unit flowsdirectly through the gas heated superheater means of the unit, thenormal communication between the gas'heated superheater means and theindependent source of relatively low pressure steam being shut off, andthe normal conmiunication for high pressure steam flow to the initialsuperheating stage and the normal communication for the flow ofcondensate from the initial superheating stage of the relatively lowpressure steam being likewise shut off. Under these circumstances thenon-radioactive steam generated in the normally high pressure steamgenerating section may act as a washing agent to wash out or diluteradioactive deposits in the superheating means and other parts of thepower plant such as the condenser and feed-water heaters. The invention,as indicated immediately above, may be considered as providing for thecontinuous service of the unit involving the high pressure steamgenerator and the gas heated superheating means normally forsuperheating relatively low pressure steam, rather than necessarilyshutting down the whole power plant when the reactor is shut down. Thisdecreases the chance of oxygen pickup in the system, and resultingcorrosion. The invention may thus involve a substantial decrease in theoriginal cost of the power plant by permitting the use of carbon steelin the feedwater heaters and associated equipment, in place of stainlesssteel, the cost of which is many times that of the carbon steel.

The invention will be clearly and concisely set forth in the claimsappended hereto, but for a more complete understanding of the invention,its advantages and uses, reference should be had to thefollowingdescription'which refers to the attached drawing, showing a preferredembodiment of apparatus involved in the invention.

The drawing is a somewhat diagrammatic side sectional view indicatingthe high pressure condensing steam generating unit involving gas heatedsteam superheating means which normally functions solely to superheatrelatively low pressure from an independent source.

In normal operation of the unit shown in the drawing, low pressure(i.e., 350 p.s.i.-a. or 600 p.s.i.a.) steam from an independent source10, such as a nuclear reactor, passes through the line 12 to the inlet14 of the first superheating stage. Here the relatively low pressuresteam is superheated by indirect heat transfer in the heat exchanger 16.This heat exchanger receives, through the conduit 18, high pressuresteam (i.e. 2400 p.s.i.a.) from the steam and water drum 20 of the highpressure steam generating system or section, of the fuel firedsuperheater. This high pressure steam passes to the inlet chamber 22 ofthe heat exchanger 16, and then through a plurality of spaced tubes 24having their inlet ends fixed within the tube sheet 26 and their outletends fixed within the tube sheet 28. The outlet ends of these tubescommunicate with the intermediate high pressure steam chamber 29 fromwhich the high pressure steam (or its condensate) passes through aseries of spaced tubes 30 to the condensate outlet chamber 32. Thecondensate of the high pressure steam flows from the chamber 32 throughone or more conduits 34 to the Water space of the drum 20.

The tubes 24 and 30 are disposed within a hollow cylinder shell 36 whichreceives the low pressure steam through the inlet 14. This low pressuresteam is initially superheated in the heat exchanger 16 from which it isconducted through one or more conduits 38 to a second superheatingstage. The shell 36 of the heat exchanger 16 is in pressure-tightrelationship with the tube sheets 26 and 28 at the opposite ends of theheat exchanger.

The steam initially superheated in the heat exchanger 16 passes throughthe conduits 38 to the horizontal header 40. From this header the steamflows through a row of of the horizontalgas pass 44 of thelunit. Theflow then continues through the upright and widely spaced screensections 46 and 48 between which the heating gases exit from the gaspass and then how past the dampers 50 into the flue '52 leading to theair heater/54. From-the upright screen sections 46 and 48, the steamflowrcontinues through the gas pass floor tube sections 56 to the header'58. From this header, the steam flows through a series of connectingtubes such as 60'to sidewall headers, one of which is indicated at 62.Leading upwardly from each of the side wall headers such as 62,.there'is a row of superheater wall tubes '64. The upper and outlet ends ofthese tubes are connected to dischargeinto'one of the upper sidewallheaders 65. Fromthesesidewall headers, the steam passes throughconnecting tubes 66 and 68i to the header 70 from which the steam flowsdownwardly through the inlet tubular sections 72 of closely spaced andserially connected return bend tubes. constituting the banks 74 and 78of convection superheater tubes; the outlet sections 80 of which arein-communication with the.

header 82.

From the header 82, thesteam flow continues downwardly through one ormore conduits 84 to-the header means or header section 86. This headermeans may include four connected header sections one 'of which islocated along each of the 4 sides of the furnace chamber 88. 'I'heseheader sectionsare preferably connected so that they all receive steamthrough the conduits 84,

one of the header sections being indicatcd"a t st the front wall 9210fthe furnace'chamber and opposite'the header section 86 disposed adjacentthe rear furnace tubes, the first sections 42 of which extend along theroof the separated water passes header 142;

- 'The lower headers for the cyclonefurnace; such as l r the header 152,are directly connected by circulators 154,

that the tubes forming parts of the walls of thecyclone furnacehavetheir outlet ends connected to one 'or more chamber wall 94. Fromthe header sections suchv as 86 and 90,, the steam flows upwardlythrough radiant. superheater 'wall tubes alongthe walls ofthefurnacechamber 88,-some of these tubes being indicated at 96 and 98.

The flow of steam continues through these tubes to the V header 100 fromwhich thejsteam flows as indicated by nace chamber-88;. r

headers such as 156, the :latterfbeing directly connected and watermixture receiving by the risers'158 to the steam space of the drum20k Vt a The refractory covered floor 160 of the primary furnace chamber1-361includes1 the floor tube sections 162 of some of the steamgenerating tubes leading directly from the drum or headeri1 42 along thefloor and then along the wallcornponent 164 'of the primary furnacechamber} Thence these, tubeslead through the walls of the threat 1 134and then through the wall component 1660f the primaryfurnacejchamber.Other-tubes directly connecting the drum or header 142 and the headermeans 144 involve the screen sections 138 and also successive tubularsections in the wall l68 separating the primary furnace chamber 136 fromthe lower part of the secondary furu;ThesidewallEheaders/170 for theprimary furnace chamber and;;the1lower'part of 'thersecondary furnacechamber are appropriately connected by circulators 172with-theheader:orqdrumi142, and the wall tubes extending upwardly fromthe headers. 170 to sidewall" headers such as the header sectionsi144-and 146 adjacent the level 140 .are preferably covered on theirfurnace sides with high temperature refractory thermally andmechanically maintained therein by metallic studs secured tothetubesin;-good-heat transfer relationship and extending into the refractorymetalin the manner, indicated in the patentto Bailey 2,239,662 of April22, 1941. i o

Others bf'the tubes leading upwardly from the lower drum or header 142include the wall tube sections-174 disposed along the rear wall 176 ofthe lower portionofe the secondary furnace chamber 88 and joined attheir upper ends to'ithe header section '146. r

a The superheater headers above thefurnace chamber 88 then flows, asindicated by the arrow 11 2.,to the header 1 108 through the connectingtubesf114. From the header 103, the steam flows through a multiplicityof spaced and serially connected return bend tubes constituting thebanks of secondary superheateru tubes 116-1-18. The

outlet ends of these tubes are connected to the header 120 from whichthe highly heated superheated steam flows through one or more conduits122, to a stage of a steam turbine. I v

The unit shown in the drawings includes a coal-fired cyclone furnacepreferably of the type shown in the US. Patent to Kerr et al. 2,594,312of April 29, 1952. High temperature furnace'gases pass from this furnaceand above the horizontal 'gaspass44, and the tubular-connections betweenthoseheaders' are enclosed within a cas- V ingwhich is preferably gastight and which is constructed.

sons to aiford thermal insulation. This casing is indicated 1 in thedrawing as having a' roof section 200, a rear wall section 202,'drumenclosing sections 204 and 206, the section 208 at the base of thehorizontal gaspass, and other 7 sections including those along the'walls92-and 94 and the sections above'the lowerlpa'rt of the ,unit includingthe through its throat 134 into the primary'furnace chamber 136 andthence across the steam generating screen tubes the lower rear wall ofthe secondary furnacev including steam generating tubes. Above the level140, the walls of the secondary'furnace chamber are lined with radiantsteam superheater tubes'as previously indicated, and below the level140' the Walls of the primary furnace cham-' 138 into the secondaryfurnace chamber 88, the walls of l the cyclone furnace, the primaryfurnace chamber 136 and.

cyclone furnace and the primary furnace chamber 136. The enclosure-forthe'pressure parts is supported from steel 7 work including suchelements as the columns 220' and 222 and the; girder'224. i The pressureparts such as the drum,

headers and tubes are supported on the steel workin manners well knownin the art, by means of hangers and drum straps. V o I r The normaloperation of the described unit involves the flow of steam at pressuressuch as 350 'p,s.i,a. or 600 p.s.i.a'; from a nuclear-reactor, the, flowof steam continu ing through the different stages of superheatingincluding the initial superheating in the heatexchanger 16 and thesubject to the fluid separating action of steam and water 7 separatorspreferably of the type shown in the U.S. Patent to Rowand et a1.2,289,970 of July 14, 1942, and,

subsequent super'heating changes inthe gas heated superheater componentssubj'ect to the heat of the gases originating in the cyclone furnace;130. The steam superheated to a temperature of-the order of'1,100'F.passes'to a stage "of'a plural stage steam turbine for producing power.l

However, to provide fora supply of steam from mama to the turbine forpower generating purposes when the nuclear reactor is shut down,theinvention involves means wherebyusteam generated in the lower part ofthe unit is passed directly to the gas'heated superheater components andthence to 'the turbine. The means for accomplishing this involves one ormore conduits such as 250 arranged through one or more large diameterdown'comers such as to the lower drumor to conduct steam from the drum20 to the superheater inlet header 40. As shown, the conduit 250 leadsfrom the conduit 18 at a position between the drum 20 and the valve 252which is closed when the nuclear reactor is shut down. Under thesecircumstances, the valve 254 in the line 34 and the valve 256 in theline 38 are closed and the valve 258 in the line 250 is open. Underthese circumstances, the pressure of the steam leaving the drum 20 isreduced to a pressure as that corresponding to the normal pressure ofthe steam from the nuclear reactor. In addition to providing for theproduction of power when the nuclear reactor is shut down, the method ofoperation of the invention provides for advantageous utilization ofnon-radioactive steam generated by the unit. This steam may act as awashing agent to wash out or dilute radioactive deposits in thesuperheaters, turbine, condenser and feedwater heater. It also decreasesthe chance of oxygen pickup in the system, and resulting corrosion andthereby provides for a substantial saving in the original cost of thesystem in that carbon steel may be used in place of stainless steel forthe feedwater heaters and associated equipment.

' When the steam from the fuel fired generator passes to the turbine,the furnace wall steam generating tubes are supplied with feed water atan appropriate temperature. This may be attained by aconvection-economizer interposed relative to the air heater 54 and theconvection superheater, the flow of feed water from the economizer beingdirected to the nuclear steam generator when the superheaters receiveonly steam from the latter generator.

Whereas the invention has been described with reference to the detailsof a specific embodiment, it is to' be appreciated that the invention isnot to be considered as limited to all of the details thereof. It israther to be considered as of a scope commensurate with the scope of thesubjoined claims.

What is claimedis:

1. A method of operating a nuclear steam generating plant including afuel fired unit normally generating steam at a much higher pressure thanthe nuclear produced steam and superheating the nuclear produced steamin an initial stage by condensing the high pressure steam and utilizingthe heat of the combustion gases to superheat the nuclear produced steamin plurality of later stages to a high temperature, comprising the stepsof reducing the pressure of the steam generated at the high pressure,bypassing the reduced pressure steam around the initial stage of thesuperheating of nuclear generated steam when the generation of nuclearproduced steam is ceased, and conducting the steam of reduced pressuredirectly through the gas heated superheater to wash the gas heatedsuperheater free of any radioactive particles deposited therein duringthe final superheating stage of the nuclear generated steam.

2. In the operation of a power plant including nuclear means fornormally generating relatively low pressure steam, a fuel fired steamgenerator and superheater for normally generating high pressure steamand condensing that steam in an initial stage of superheating thenuclear generated steam in its passage to a point of use, the fuel firedsuperheater also involving a gas heated second stage of superheating thenuclear generated steam; the method of operation which includessupplying steam from the high pressure steam generating section of thefuel fired superheater directly to its gas heated superheating sectionand bypassing an initial and steam condensing stage of initialsuperheating when the nuclear steam generator is inoperative to effect awashing of the gas heater superheating section free of any radio-activeparticles deposited therein during the second stage of superheating thenuclear generated steam.

3. In a method of operating a power plant including a low pressure steamgenerating nuclear reactor, a fuel fired high pressure steam generatorfor normally superheating the nuclear generated steam by heat transferfrom the condensation of high pressure steam and from the gases of thefuel fired component, comprising effecting combustion Within a confinedzone by burning a fossil fuel at temperatures in excess of 2200 F.,transmitting heat predominantly by radiation from the active combustionzone to confined water streams thereby generating steam at a pressuremuch higher than the pres sure of the steam from the nuclear steamgenerator, transmitting heat by indirect heat exchange from the highpressure steam to the much lower pressure steam from the nuclearreactor, said transmission of heat involving the condensing of the highpressure steam, returning the condensate to the inlets of the waterstreams subject to the heat of the active combustion zone, furthersuperheating the low-pressure steam from the condensing zone by heattransmission from the combustion gases to confined streams of the lowerpressure steam in a heating zone beyond the active combustion zone in agas flow sense, and when the nuclear reactor is shut down, by passingthe condensing zone and superheating the steam from the normally highpressure steam generator by passing it through the gas heatedsuperheating zone.

4. In apparatus of the character described, means for generatingrelatively low pressure steam, said means being a steam generatingnuclear reactor, high pressure steam generating means including a fuelfired furnace having steam generating wall tubes, means for initiallysuperheating the lower pressure steam from the nuclear reactor bycondensing the saturated steam from the high pres sure steam generatingmeans, a condensate line for returning the condensate from saidsuperheating stage to the Water space of the high pressure steamgenerating means, means including a separately fired gas heatedsuperheater incorporated as a unit with the high pressure steamgenerating means and subject to the heat of the gases from the fuelfiring, a superheated steam supply line leading from the firstsuperheating stage to the sep: arately fired superheater, means forconducting the superheated steam to a point of use, and means bypassingthe initial superheating stage and conducting steam from the highpressure steam generator directly through the separately firedsuperheater to said point of use when the supply of steam from thenuclear recator steam generator is shut off.

5. The combination of claim 4 wherein said last named means includes theshut-off valves in the high pressure steam line leading to the initialsuperheating stage and in the condensate return line from the initialsuperheating stage to the high pressure steam generator, and a valve inthe by-pass line leading directly from the highpressure steam generatingsection to the gas heated superheater.

6. In an apparatus of the character described, means for generatingrelatively low pressure steam, another steam generating means includinga furnace for effecting the combustion of a fossil fuel to generate arelative high pressure steam, a heat exchange means connected to saidlower pressure and high pressure steam generating means wherein the lowand high pressure steam generated by said steam generating means,respectively, are brought into indirect heat exchange relationshipwhereby said low pressure steam is superheated and said high pressuresteam condensed, a secondary superheating means exposed to the productsof combustion of said fossil fuel, said secondary superheating meansbeing connected with said heat exchanger means to receive the lowpressure superheated steam from said heat exchanger means and exposesaid low pressure superheated steam in heated transfer relationship withthe products of said fuel combustion so as to highly superheat said lowpressure superheat steam; and a valved bypass means disposed betweensaid high pressure steam generator and said heat exchange means andconnecting said high pressure steam generating means to said secondarysuperheating means whereby steam generated by said combustion of fossilfuel is selectively directed through either said heat exchanger means orsaid secondary superheating means.

7' a 7,. In a steam generating and heating arrangement, a first steamgenerating means adapted 'to selectively pro duce relatively highpressure steam and low pressure steam and including 'a furnace chamberhaving walls of steam generating tubes, fossil fuel burning meansarranged to discharge heating products of combustion into said furnacein heat absorbing relationship with said generating tubes, a steam andwater separating drum connected to said generating tubes for receivingeither the high pressure or low pressure saturated steam generated insaid tubes, said drum having a steam outlet, a second steam generatingmeans producing relatively low pressure saturated steam, said secondgenerating-means being adapted to be operatively' or inoperativelyconnected into said arrangement, a' heat exchange means in commu'nieation with said drum outlet-and said'second' generating means, saidheat exchange means adapted to receive in indirect heat tr-ansfer'relationship the high pressure steam of said'first generator means and therelatively low pressure steam of said second generator means wherebysaid low pressure steam is initially superheated and said high pressuresteam condensed, a secondary superheating means exposed -to thecombustion products of said furnace and heated thereby, a first meanscon necting said secondary superheater in communication with saidheatexch-ange means whereby said superheated low pressure steam fromsaid heat exchanger is delivered to said secondary superheater means tobe highly superheated therein, a second means directly connecting saiddrum outlet to said secondary superheating means, and

valve means operatively disposed in saidfirst and second s nace foreffecting the combustion of a fossil fuel to gen erate a relative highpressure steam, 3' heat exchange means connected to said low pressureand high pressure steam generating means wherein the low and high pressurefste-am generated by saidstearn generating means respectively arebrought-into indirect heat exchange-relationship whereby said lowpressure nuclear react'ongen erated steam is superheated and said fossilgenerated'high pressure steam condensed, a secondary 'superheating meansexposed to the products of combustion of said fossil fuel, saidsecondary supe'rheating means being con nected with said heat exchangermeans to receive 7 superheated steam therefrom and to 'expose saidsuperheated steam in heated transfer relationshipwith theproductsoffsaid fuel combustion so as to be highly superj heated thereby, andbypass means directly connecting i said second mentioned steamgenerating means to said, secondary superheating means whereby the steamgenenated by said combustion of fossil fuel is directed there to, andmeans for rendering saidbypass operative when said nuclear reactor meansis rendered inoperative wherebythe flow of the fossil generated steamthrough the secondary superheater'effectsa cleansing action of saidsecondarysuper'heating means, 7

References Cited in file of this patent UNITED STATES PATENTS FOREIGNPATENTS, Great Britain 1Sept; 10,1952

679,083 V OTH ER REFERENCES Nucleonics, pp. 42-43, January 1953. a v

Facts About Con. Edisons lndian Point Nuclear El ectric GeneratingStation; September 19 55, pp; 1- 4. (Copy.

in Class 204193.2R.)

